The present invention relates generally to a variable cam mechanism and more particularly to a mechanism for varying the characteristics of a cam for controlling the opening and closing of valves in an internal combustion engine according to the speed of the engine.
Since the more advanced development of internal combustion engines it has been recognized that greater power outputs and efficiencies can be achieved if intake and exhaust valve operation can be varied as a function of engine speed. The open time duration of a valve, with respect to the cycle time of the piston, is desirably greater at high engine speeds than it is at low engine speeds. One way to accomplish a variation in valve timing in engines where the poppet valves are controlled by the rotative position and contour of cams on a revolving camshaft is to vary the effective width of the lobe of the cam which is responsible for lifting the valve to an open position.
The U.S. Pat. Nos. to Horine and Hellmann, 1,757,046 and 2,888,837, respectively, disclose apparatus relating broadly to variable nose cams for a similar purpose. The more pertinent prior art, however, is found in U.S. Pat. No. 1,175,395 to Wixon, French Pat. No. 1,109.790, and German Pat. No. 2,921,645. These three patents disclose inventions utilizing cam pairs acting in concert to effect a variation in cam lobe width. The French and German patents disclose devices to counterrotate both cams in the pair. The French patent utilizes concentric splined shafts and the German patent utilizes a sliding rod with pins to effect the rotation. Although the Wixon patent discloses a pair of adjacent cams, only one member of the pair is rotatable relative to the camshaft. Further, the cams in Wixon's invention that are rotated, are rotated by means of slot segments on the camshaft, each of which is adapted to only one cam pair. This design, as opposed to the present invention, necessitates the use of keys and limits the possible cam variation.
Although various aspects of these disclosures are similar to the present invention, none of them contains the features necessary to be a practical adjunct to today's production engines.